1. Field of the Invention
The present invention is directed generally to a planar optical display, and, more particularly, to a high contrast front projection display panel and a method of making a high contrast front projection display panel.
2. Description of the Background
Video display screens typically use cathode ray tubes (CRTs) for projecting an image onto the outlet face of the screen. A typical screen of this type has a width to height ratio of 4:3 with 525 vertical lines of resolution. An electron beam must be scanned both horizontally and vertically on the screen to form a number of pixels, which collectively form the image. Conventional cathode ray tubes have a practical limit in size and are relatively deep to accommodate the required electron gun. Larger screen televisions are available which typically include various forms of image projection for increasing the screen image size. However, such screens may experience limited viewing angle, limited resolution, decreased brightness, and decreased contrast, particularly in display screens using front projections. This is, in part, due to the use of white screens to allow the screen to reflect the front projection back to the user. Thus, because the screen is white, the darkest black level that can be displayed is “screen white”, the color of the screen when the projection is off, due to the fact that black light cannot be projected. Consequently, the projection must be either on, or off, to produce white, or black, respectively. Thus, where black is viewed on a front screen projection system, the viewer is actually seeing the white of the background, i.e the absence of projected light, which the human eye sees as black in the context of the white light projected elsewhere on the background, meaning that the presence of the optical spectrum projected onto the white background forms a “whiter than white” color, which the eye sees as white. This is the reason that a room must be darkened in order for a viewer to see black on a front projection screen.
Optical panels can be created using a plurality of stacked waveguides, and may be rendered black using at least one black cladding layer between transparent cores of the waveguides. The cladding layers disclosed therein have a lower index of refraction than the waveguide cores for effectuating substantial internal reflection of the image light channeled through the cores, and thereby improve contrast, i.e. thereby improve the appearance of black images on a screen. Such optical panel displays have typically been operated in a rear projection mode.
Therefore, the need exists for a display panel that allows for front projection, while also providing the appearance of a black screen to improve viewing contrast and to eliminate the need to dim lights in order to allow a viewer to see black images.